Presented is are methods that enable linearly-polarized ground terminals to access circularly-polarized channels through wavefront multiplexing techniques. This invention comprises conventional ground terminals, a unique polarization alignment processor on the transmitting side and feedback channel. As a result of this invention, teleport operators can gain greater flexibility in how they manage their assets, and so can users in how they access available communication resources.
This invention also relates to methods that anneal the interference of undesired circularly-polarized signals to the intended channel. A probing signal known to feedback terminals is exploited such that the differentials in signal propagation paths can be equalized by the unique polarization alignment processor and the interference due to undesired signals is annealed.
Field of the Invention
The present invention relates to methods for enabling linearly-polarized (LP) ground terminals to access circularly-polarized (CP) channels. It is also related to wavefront multiplexing/de-multiplexing (WF muxing/demuxing) technologies.
The present invention relates to radio frequency communication devices and communication architectures that comprises ground terminals, communication assets and channels. More specifically, this invention allows ground terminals with linear polarization format to communication with communication assets of circular polarization format via wavefront multiplexing techniques. This offers tremendous advantages including, but not limited to, improved flexibility and increased efficiency of existing assets.
Description of the Prior Art
It is common practice in utilization of communication links to equip terminals and communication assets with antennas of compatible polarization formats. It is generally true that LP terminals access LP channels, and CP terminals access CP channels. One says that linear polarization and circular polarization are incompatible polarization formats. As the asset changes its polarization format, so does the terminal accordingly. This happens, for instance, when LP terminals switch services from a provider with LP satellites to another one with CP satellites. Then the antenna polarization formats require reconfiguration from LP to CP. One main reason to reconfigure polarization formats is to prevent 3 dB signal-to-noise ratio (SNR) loss due to polarization incompatibility between the ground terminals and the communication assets. The radiation patterns emanating from LP terminals and incident on CP assets have also been treated “unintelligible”, or interference/noise, which also serves as a second reason that the polarization formats of terminals and transponders remain compatible in conventional communication architectures.
Linear polarization has two complimentary formats, one of which is vertical polarization (VP) and another is horizontal polarization (HP). Signals conditioned on these two formats have 90 degree difference in space. Specifically, a signal with VP format has electrical field aligning with the vertical direction; and a signal with HP format has electrical field aligning with the horizontal direction. The vertical direction represents 90 degree difference with respect to the horizontal one. One should note that the vertical and horizontal directions are both defined with respect to the direction of electromagnetic wave propagation. In free space, the wave moves along the line perpendicular to said vertical and horizontal directions.
Due to the particular said configuration of electromagnetic wave propagation directions, it is essential for ground terminals and communication assets in conventional architectures to be aligned in their polarization. In other words, for LP ground terminals and LP assets to communicate successfully, their VP directions need to be aligned and so do their HP directions.
As the VP and HP signals have identical strength but exactly 90 degree difference in time, the overall effect stimulates an electrical field that rotates in space with respect to the propagation direction. The VP signal may have 90 degree in advance of or behind the HP one, which results in right-hand circularly polarized (RHCP) or left-hand circularly polarized (LHCP) formats. RHCP and LHCP are two complimentary formats of circular polarization.
The main property of a CP signal is its handed-ness, which can be RHCP or LHCP. For CP ground terminals and CP assets to communicate successfully, their VP and HP directions need not be aligned respectively. In other words, there is no stringent requirement of aligned polarization in CP communication links as seen in LP ones. On the contrary, there are tremendous advantages of enabling LP ground terminals to access CP communication assets, thanks to the considerable reduction in the cost of mechanically realigning polarization.